Glasses suitable for production of copper-coated glass-ceramics

ABSTRACT

Provided are three distinct crystallizable copper-bearing alumina-silicate glass compositions. When heat treated during or subsequent to crystallization in an oxidizing atmosphere a copper oxide layer is formed upon the surface of the glass. Subsequent reduction of this layer to a metallic copper results in a strongly adherent film of copper upon a glass-ceramic substrate which may be further processed for use in microelectronic devices and printed circuit boards. The compositions, either crystallized or in vitreous state, are easily drilled using ultrasonic techniques. When such holes are formed prior to heat treatment, subsequent oxidation and reduction results in the copper film extending through the holes, thus providing a conductive lead from one side of the ceramic substrate to the other.

United States Patent 1191 Pirooz Apr. 9, 1974 15 1 GLASSES SUITABLE FORPRODUCTION OF 3,557,576 1/1971 Baum 65/33 C0PPER COATED GLASSCERAMICS3,231,456 1/1966 McMillan et a1. 106/52 X 2,733,158 1/1956 Tiede 106/52X [75] Inventor: Perry P r Toledo, Ohio 3,490,887 1/1970 Herczog et a165/33 [73] Assignee: Owens-Illinois, lnc., Toledo, Ohio PrimaryExaminer-Helen M. McCarthy 1 1 Filed: 23, 1971 Attorney, Agent, 01'FirmChar1es S. Lynch; E. J. 211 App]. 190.; 118,201 Holler 521 11.5.0106/52, 29/569, 65/32, 1571 ABSTRACT 65/33, 106/39.7, 106/39.8, 106/53,106/54, Provided are three distinct crystallizable copperll7/227. 161/16. 252/512 bearing alumina-silicate glass compositions. When [51] Int.Cl. C03c 3/22, C03c 3/30 heat treated during or subsequent tocrystallization in [58] Field of Search 106/39 DV, 52, 53, 54. anoxidizing atmosphere a copper oxide layer is /39-6, 39- 5/32, 33, 21;252/300, formed upon the surface of the glass. Subsequent re- 506, 512;317/258; 29/569; 161/196 duction of this layer to a metallic copperresults in a strongly adherent film of copper upon a glass-ceramic [56]References Cited substrate which may be further processed for use inUNITED STATES PATENTS microelectronic devices and printed circuitboards. 3,528,828 9/1970 Smith 106/39 13v The Compositions ,either,rystamzed 9 f 3.205.079 9/1965 Smokey v I 06/39 Dv state, are easilydrilled using ultrasonic techntques. 17331 H1964 Henry et aL 106/39 vWhen such holes are formed prior to heat treatment, 3, 40,661 3/1966Babcock 65/33 subsequent oxidation and reduction results in the cop- 2972,543 2/1961 Beals et al. 106/48 per film extending through the holes,thus providing a 3 586,521 6/1971 Duke l06/ conductive lead from oneside of the ceramic sub- 3,464,806 9/1969 Seki et a1. 65/32 t t t th th3,420,645 1/1969 Hair 1 65/21 2,920,971 1/1960 Stookey 106/39 DV 7Claims, N0 Drawings GLASSES SUITABLE FOR PRODUCTION OF COPPER-COATEDGLASS-CERAMICS This application relates to crystallizable glasscompositions and methods of using same. More particularly, thisinvention relates to glass compositions capable of forming, in situthereupon, a copper layer useful in the microelectronic and printedcircuitry art.

Patterns of conductor metals, such as copper, have long been used inthemicroelectronic and printed circuit arts such as for making multileadconductor patterns in integrated circuitry packages or for makingprinted circuit boards. Generally speaking, such patterns are formed by,at least initially, providing a separate layer of the conductor metalupon a separate substrate and thereafter attempting to adhere the twolayers together. While somewhat successful, a major problem in the arthas been to obtain a substrate material which is sufficiently compatiblewith the known conductor materials to provide good adhesion withoutunduly sacrificing other necessary mechanical and electrical properties.That is to say, while several materials have been developed which arecompatible with conductor materials, they generally sacrifice othermechanical (e.g. high temperature strength) and electrical properties inorder to attain compatibility. On the other hand, other materials haveachieved mechanical properties and electrical properties but they areusually achieved only at the expense of compatibility and the ability toobtain adhesion especially under humid or high temperature conditions.

One approach for solving this problem has been to develop a glassceramic substrate, which upon selected heat treatment will causeconductor metal ions within its composition to migrate to its surface.This in situ conductor surface layer formation with ceramics ofrequisite expansions generally achieve good adhesion and hightemperature strength characteristics. Such an approach is exemplified byU.S. Pat. No. 3,231,456. In this patent two specific types ofcopper-bearing, phosphorus pentoxide nucleated glasses are heat treatedfirst in an oxidizing atmosphere under closely controlled conditions tocrystallize the glass and to cause migration of copper ions to thesurface of the glassceramic so formed. Thereafter, the glass-ceramic isheat treated under tightly controlled conditions in a reducingatmosphere to form a conductive copper film on the surface. Such acopper film is coated with a thin siliceous insulating layer and beforeuse as a conductive device, the siliceous layer must be removed as forexample with an HF etch. While achieving, generally speaking, goodadhesion due to in situ copper migration, the need for an HF etch addsadditional expense to the process. Furthermore, and as will be morefully illustrated hereinafter, the film was essentially nonconductive.

U.S. Pat. No. 3,490,887 also discloses the ability of copper ions tomigrate to the surface of a glass ferroelectric material and form, afterheat treatment in a reducing atmosphere, a metallic copper conductivecoating thereupon. This patent, of course, deals with ferroelectricmaterials generally of the rather exotic barium titinate and niobatetype, which materials are difficult to make under the best of controlledheat-treatments. Furthermore, because of the difficulty of forming largestructures from these and other ferroelectrics and because of otherfactors such as cost of materials, etc.,

such materials are generally notisuitable for use as microelectronicsubstrates or printed circuit boards.

In view of the above, it is apparent that there exists a definite needin the art for new glass compositions which can be used in themicroelectronic and printed circuit arts to overcome the stated problemsexperienced therein.

Generally speaking, this invention fulfills this need in the art byproviding certain copper-bearing crystallizable glass compositions ofthe alumina-silicate type which are capable of mechanically andelectronically performing as substrates in the microelectronic and/orprinted circuitry art and which are capable of forming, in situ duringheat treatment, a tightly adhered conductive copper surface layer not.overcoated with a siliceous insultating layer. As another aspect of thisinvention there is provided a process of using these glass compositionsto form substrates having holes therein which are insitu copper coatedto electronically connect selected portions of different sides of thesubstrate. Such a process finds unique applicability in formingsubstrates for flip chip or beam lead integrated circuit packages asmore fully described hereinafter.

' The copper-bearing crystallizable glass compositions contemplated bythis invention are alumina-silicates generally classifiable into threetypes as follows:

Preferably, at least about by weight of the composition is made up ofSiO A1 0 CaO, Na O, TiO CuO, and K 0 if present. A particularlypreferred glass composition of Type I consists of:

Glass Composition A Constituent Approx. Wt.

SiO 30 M 0 l0 MgO 4 CaO 6 82:0 2 ZrO, 3 TiO, 20 CuO 5 Na O l5 K 0 5Properties of Product (Cu layer about 1-3 mils thick) Coeff. of Exp. (X10'' cm/cm/"C O-SOOC) glass 1 l0 glass-ceramic 128 sheet resistance(ohms/sq.) 0.028 solderability excellent adhesion (stand. pull test lbs.7.6

pull 0.] in pad) dielectric constant (K) 21.3 dissipation factor (D)19.2

loss factor (K X D) 4.l

pred. cryst. phase NaCa silicate Coeff. of exp. (X 10" cmlcm/C) 35 glass73 glass ceramic TYPE [1 Glass Composition C-Continued ConstituentApprox. Wt. Constituent Approx. Wt.

1% 32 5 iii iiffiiiiii N21220: F20 3-6 adhesion (stand. pull test, lbs.,0.1" pad) K O 5 6.7 d electr c constant (K) Na,O K10 20 0-86 dissipationfactor (D) Tioz 1045 0.057 loss factor (K X D) cuo Predominantcrystalline phase high Other compatible oxides 0-10 10 15 332 sol.

Examples of other compatible oxides include PbO, B 0 Li O, SnO, MgO, ZrOCaO, BaO, and the like. Preferably, however, no other oxides areemployed. A 15 The glass compositions of this Q Y be particularlypreferred glass of Type II consists of: ed from conventional batchingredients and formed Glass CompoSition'B into desired shapes usingstandard techniques As alluded to heremabove, the glass compositions ofConstimem Approx wt this invention in shaped-glass form are readilyconverted into copper layer bearing glass ceramics by subsio 45.4jecting them to a heat treatment. In a preferred tech- ?gg Q2 nique, thefirst step in the heat-treatment is to subject CuO 5.0 the glassstructure to an oxidizing atmosphere (e.g. air, N310 165 oxygen, ormixtures thereof) at a sufficient tempera- Pmpernes of Product, (Culayer=abut thick) 2 5 ture and time to cause migration of copper ions tothe surface to form a significant layer of CuO thereon. (X (Homo Such atreatment may be effected after crystallization glass ceramic 110 or beused to simultaneously effect crystallization of Sheet q) 0-022 theobject. Thereafter, the glass-ceramic structure is zz s ii' z' i pun MLOJ inch d subjected to areducing atmosphere or environment at pad) atemperature usually lower than that of the first heattreatment and forasufficient period of time to reduce IUSK factor (K x D) 0.x? the CuO toa conductive layer of metallic copper. MM As stated this two-step heattreatment is preferred because it appears to optimize the quality of thelayer so formed. This is not to say, however, that it is critical. TYPEActually a one-step heat treatment may be used wherein crystallization,ion migration, and reduction Constituent pp are all carried out in areducing atmosphere. Such a Siog 4040 one-step technique usually isconducted at a higher A110,, 20-30 temperature than the reducing stepof. the two-step 2% 5:5 technique in order to insure thatcrystallization takes v M80 5-3 place. Generally speaking, this one-steptechnique usufigu ZIO gfi about 6% ally results in a thinner, moreporous film of metallic Conipatible oxides 0-10 copper. In thoseinstances where such a layer is tolerable, economics may render thisone-step technique more desirable. Examples of Compatible Oxides include2 PbO, Different times and temperatures for the heat treat- B203! B110,t Well known itl the A P ments are preferably employed for each type ofglass. y Preferred glass composition of yp consists of! ln thoseinstances where the geometrical tolerances are critical it is oftenpreferred to precrystallize the glass Glass Composition C prior to thecutting and grinding operations of the parts in order to avoid therather inaccurate necessity of esti- Consmuem Approx mating shrinkageduring crystallization and/or encountermg camber. In those instances,however, where prei 33-; cise substrate dimensions are not required itis most 1 5 convenient for economic purposes etc., to combine the 2 3-;crystallization and oxidizing heat-treatments. Typical and preferredheat-treatment schedules for Tao, 1.7 each of the three types of glassescontemplated by this 5:8 {3 invention are as follows (assumingconventional sub- 8,0 1.0 strates of standard thicknesses): F1 TYPE 1Properties of Product (Cu layer= about 1-3 mils thick) 1. oxidation heattreatment heat in ail. oxygen, or

synthetic mixtures thereof at about 750850C, preferably about 800C, for4-20 hours, preferably 16 hours.

2. Reduction heat treatment heat in a reducing environment, preferably agaseous environment containing at least about H and most preferably aforming gas environment (90% N H at about 450-600C (preferably about500C) for about 5-60 minutes (preferably about minutes).

Type ll 1. Oxidation heat treatment same as type I above except at about800900C (pref. 825C) for 4-24 hours (preferably 16 hours).

2. Reduction heat treatment same as type I. TYPE III 1. Oxidation heattreatment same as type I above except at about 800900C (preferably 825C)for 16-64 hours (preferably 24 hours).

2. Reduction heat treatment same as type I.

In all of the above heat-treatments, the vitreous glass will beinherently crystallized during the oxidizing heat treatment step. Ifprecrystallization is desired, the oxidizing heat treatment times andtemperatures may be employed first to precrystallize and then in anadditional step after cutting, grinding, and the like to effect thegeneration of the CuO coating.

Once the compositions of this invention have been formed into asubstrate containing a tightly adherent copper in situ coatingthereupon, it may be used directly in a wide variety of environmentswithin the microelectronic and printed circuit art. Since no insulatingsiliceous layer coats the metallic copper layer upon its formation noacid etching as per the prior art is necessary. In addition, the coatingformed is of such a good quality copper that excellent solde'rabilitywith conventional conductor leads (e.g. Kovar) is obtained.

The various properties of products formed from preferred specificcompositions are given hereinabove. From this data, there may be derivedseveral generalizing characteristics for each of the three types ofglasses contemplated by this invention. Firstly, the compositions ofType I, and particularly composition A, form products which exhibitexcellent conductor characteristics, both mechanical and electrical. Onthe other hand their dielectric characteristics are not as good as thoseof Types II and Ill. For this reason it is particularly preferred to useType I compositions in those environments where high mechanicalstrengths and conduction are required but where the circuit is not beingsubjected to high frequencies and/or power densities.

One particular area in which Type I compositions find particularlysuitable use is in the flip chip package for integrated circuits.l-Ieretofore such a package had to be produced by soldering a lead frameto the conductor leads on the same side of the substrate having thesilicon integrated circuit flip chip located thereon. Now, because ofthe ability to easily form an electronically conductive hole or via fromone side of the substrate to the other, the frame may be moreconveniently connected to the side of the substrate opposite that of thesilicon chip. A typical technique for producing such a package inaccordance with this invention is to: v

a. form the desired shaped substrate having a Cu coating thereupon asper the above using any of the three types of glasses, but mostpreferably of Type I, the substrate having Cu coated holes strategicallylocated therein,

b. form the desired conductor pattern, preferably by standard photoetchtechniques in the Cu layer,

c. mount the flip chip" integrated circuit upon the conductor patternand mount a lead frame so as to connect the leads to their correspondingconductor areas on the other side of the substrate,

d. solder and seal both the lead frame and chip to the substrate, and

e. package the entire component in plastic as per conventionaltechniques.

As stated, Type I compositions are preferred in this flip chipembodiment since such packages are generally not called upon to carry oremploy high frequencies and/or power densities. On-the other hand, thepackaging-in-plastic step by its nature tends to subject thesub-assembly to shock and other maltreatment. Because of the excellentmechanical strength of the various joints and bends formed when usingcompositions of Type I, high reliability and low numbers of rejects areobtained despite this mal-treatment.

While Types II and III may also be used in the flip chip package, theygenerally exhibit lower conductor characteristics (both mechanical andelectrical) than does Type I and thus are less desirable to use. On theother hand, Types II and III generally exhibit significantly betterdielectric properties such as lower dielectric constants, lowerdissipation factors, and lower loss factors than Type I. These two typesof glass compositions are therefore usually most preferably employedwhere high conductor characteristics are of secondary importance todielectric characteristics. One example of such an environment is aprinted circuit board which must carry or employ high frequencies and/orhigh power densities. Generally speaking Type I compositions are lessdesirable to use as frequencies approach the microwave range and/orpower densities approach about I00 watts/m From the point of view of acomparison between Types [1 and Ill, Type II is intermediate betweenTypes 1 and III in both conductor characteristics and dielectricproperties. Thus this invention provides a spectrum of compositions foruse throughout the many environments of the microelectronic and printedcircuit art.

The following examples are presented by way of illustration and notlimitation.

EXAMPLE 1 The following batch ingredients were blended and heated to2,300F for 22 hours in an electric furnace using a platinum cruciblewith continuous mechanical stirring in order to form a homogeneous glassof composition A above:

The molten glass formed was cast into a preheated mold (650F) andannealed at 940F to obtain a billet .2 inches X 4 inches X 8 inches.This billet was then precrystallized by heating it in air at 800C for 16hours. The predominant crystalline phase was NaCa silicate. The billetwas then sliced using a standard saw to obtain a substrate 1 inch X 2inches 0.025 inch. The Glass-ceramic was easily cut, and the cutsurface, quite surprisingly, was so smooth that no grinding thereof wasnecessary. The sides of the substrate were then trimmed to provideprecise dimensions for later use. Holes on the order of about 8-10 milsin diameter were then provided at selected locations through the 0.025inch thick substrate using a Sheffield Cavitron (a conventionalultrasonic drill).

The so formed substrate was then heated in air at 800C for 16 hourswherein after it was cooled to 500C and the atmosphere was purged withnitrogen and then switched to forming gas (90% N 10% H The substrate wasthen held for minutes at 500C in the forming gas whereupon a' continuouseven coating of copper of about 1-3 mils in thickness was formed. Theholes were also found to be evenly coated and conductively connected thecoated sides of the substrate. The properties of the coated substrateare those reported relative to the Composition A table hereinabove. 4

This substrate, so formed may now be used in a variety of environments,two examples of which are set forth as follows:

A. Flip-Chiplackage By providing the above described coated holes in therequisite pattern a flip chip integrated circuit package ismanufacturedas follows:

a. apply to the substrate a conventional photoresist composition to thecopper coating,

b. expose the photoresist through a mask to produce the requisite latentimage for forming a conductor pattern of the copper coating,

c. develop photoresist latent image with photoresist developer,

d. etch, using a conventional etchant such as Fecl to produce Cuconductor pattern,

e. clean off masking compounds,

f. separate large substrate into individual substrates by conventionalmethods,

g. mount flip chip and attach assembly to the lead frame as describedabove,

h. seal and solder components, andv i. encapsulate sub-assembly inplastic to form package. B. Printed Circuit Board By providing asubstrate as formed except using a billet of dimensions- Z-Vz inches X2-% inches X 6 inches a printed circuit board may be readily formed.Generally speaking, after slicing, the substrate is trimmed and groundusing a 600 grit silicon carbide powder to obtain a very smooth surfaceand dimensions of about 2 X 2 X l/l6 inch. Holes are similarly providedas in A above, and photoetching as described is carried out to achievethe desired printed conductor pattern. The substrate is thenconventionally mounted in the environment in which it is to be used.

EXAMPLE ll By way of comparison and in order to show the uniquecontribution which this invention makes to the art, the procedures ofU.S. Pat. No. 3,231,456 were twice reproduced, each reproduction beingby a different individual. The compositions reproduced for evaluationwere Composition ll and VIII from the table at the bottom of page 1 ofthis patent. Each reproduction started with a separately formulatedbatch to produce each of the recited compositions. The compositions soproduced were chemically analyzed and found to be very close to theexact percentages reported in the table of the patent. For example, oneof the reproductions analyzed as consisting of:

Constituent Theoretical Analyzed SiO 63 .7 63.9 U 0 1 8.0 1 7.8 AI O10.9 10.9 P 0 4.4 4. 1 CuO 2.0 1.9 SnO 1 .0 0.96

The melting procedures employed were those outlined in column 4, lines26-32' of the patent. The following table lists the melting procedurefor both compositions:

Size of melt 500 gm. Temperature 2400F Time 6 hrs. Atmosphere airCrucible SiO Furnace electric Good glasses were obtained from bothcompositions. The following table lists the melting data:

ll Vlll seeds none none devitrif. none none homogeneity good good colorlight blue, transp. light blue, transp. surface copper oxide film copperoxide film annealing 480C (1 hr.) 480C (1 hr.)

Heat Treatment Atmosphere room temp. 0,

5C/min. rise 0 5C/min. rise 0,

600C (1 hr.) furnace purged with N, for 10 min.

Then forming gas was started.

5C/min. rise forming gas 850C (1 hr.) forming gas furnace rate coolforming gas room temperature forming gas Both reproductions yieldedsubstantially the same results. A film having the appearance of copperwas present after heat treatment in both compositions. However, a checkfor conductivity with a Simpson voltohm-milliamp meter showed noconductivity. It was therefore assumed that a thin siliceous filmcovered the copper-colored film as claimed in the patent.

Example 11 was etched for 50 minutes in two precent hydrofluoric-acid asin the patent, column 4, lines 51 through 55. While a copper-coloredfilm still remained, testing still showed no conductivity. In an attemptto remove more of the supposed siliceous layer, etching was continuedwith four per cent l-IF for another thirty minutes, but the surface wasstill not conductive. Example VIII was treated with a two per centsolution of hydrofluoric acid for minutes according to the procedureoutlined in column 5, lines 5 14 of the patent, and showed noconductivity at all, but it appeared that the colored film had beenpartially removed by the etchant.

The above comparison with the prior art amply evidences the valuablecontribution presented by this invention. Once given the abovedisclosure many other features, modifications, and improvements willbecome apparent to the skilled artisan. Such other features,modifications, and improvements are thus considered to be a part of thisinvention the scope of which is to be determined by the followingclaims.

I claim:

1. A crystallizable glass composition capable of being crystallized to aglass ceramic body which when heated in a reducing atmosphere will forman in situ metallic copper coating upon its surface, said glasscomposition being selected from a composition consisting essentially ofby weight per cent about:

A. 25-35% SiO 5-l3% A1 0 3-9% CaO, 0-7% MgO, 10-20% Na O, 0-l0% K 0,15-25% Na O K 0, 15-25% TiO 05% ZrO 3-7% CuO, and 0-5% BaO; (B) 40-50%SiO l5-25% A1 0 10-20% Na O, 05% K 0, l520% Na O K 0, 10-15% TiO and3-7% CuO; and (C) 4050% SiO 20-30% A1 0 l-10% TiO 3-7% CuO, 5-8% ZrO andat least about 6% TiO ZrO 2. A glass composition according to claim 1wherein said composition is (A) wherein at least about by weight of saidcomposition is made up of SiO A1 0 CaO, Na O, TiO K 0, and CuO.

3. A glass composition according to claim 1 wherein said composition is(B) and wherein said composition contains no more than about 10% byweight of other compatible oxides.

4. A glass composition according to claim 1 wherein said composition is(C) and wherein said composition contains no more than about 10% byweight of other compatible oxides.

5. A glass composition according to claim 1 which consists essentiallyof by weight, about 30% SiO 10% A1 0 4% MgO, 6% CaO, 2% BaO, 3% ZrO 20%TiO 5% CuO, 15% Na O, and 5% K 0.

6. A glass composition according to claim 1 which consists essentiallyof by weight, about: 45% SiO 21% A1 0 12.5% T10 5% CuO, and 16.5% Na- O.

7. A glass composition according to claim 1 which consists essentiallyof by weight, about: 43.5% SiO 28.5% A1 0 0.6% Li O, 6.6% MgO, 3.8% BaO,6.6% ZrO 1.7% TiO 5.0% CuO, 1.9% PbO, 1.0% B 0 and 0.9% F

" UNITED STATES PATENT OFFICE 569 CERTIFICATE OF CORRECTION Patent No.3,802,892 Dated April 197 Inventor(s) l-"Y irooz It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Col. 2, line16, "insultating" should be ---insulating---. Col. 6, line37 ",in. should be ---in. Col. 6, line 66, after the word "glass" insert---s0- Col. 7, line after the word "standard" insert -diamond---. Col.9, line "precent" should be ---percent---.

Col. 10, Claim 1, line 7, "543% 2:0 should read.-- -5-8% M 0, 045% ZrOSigned and sealed this 31st day of December l'974.

(SEAL) Attest:

McCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer. Commissioner ofPatents

2. A glass composition according to claim 1 wherein said composition is(A) wherein at least about 90% by weight of said composition is made upof SiO2, A12O3, CaO, Na2O, TiO2, K2O, and CuO.
 3. A glass compositionaccording to claim 1 wherein said composition is (B) and wherein saidcomposition contains no more than about 10% by weight of othercompatible oxides.
 4. A glass composition according to claim 1 whereinsaid composition is (C) and wherein said composition contains no morethan about 10% by weight of other compatible oxides.
 5. A glasscomposition according to claim 1 which consists essentially of byweight, about 30% SiO2, 10% Al2O3, 4% MgO, 6% CaO, 2% BaO, 3% ZrO2, 20%TiO2, 5% CuO, 15% Na2O, and 5% K2O.
 6. A glass composition according toclaim 1 which consists essentially of by weight, about: 45% SiO2, 21%Al2O3, 12.5% TiO2, 5% CuO, and 16.5% Na2O.
 7. A glass compositionaccording to claim 1 which consists essentially of by weight, about:43.5% SiO2, 28.5% Al2O3, 0.6% Li2O, 6.6% MgO, 3.8% BaO, 6.6% ZrO2, 1.7%TiO2, 5.0% CuO, 1.9% PbO, 1.0% B2O3 and 0.9% F2.